I have a Yeong Chin Supermax (Bridgeport clone) circa 1989. It has servo dynamics motors and amps.
motors (MT30U4-42)
amps SDF-1525-12
The machine has been retrofit to linuxcnc using Mesa 5i25/7i77 control. It's been running this way for a couple years.
Recently the Y axis started making a loud growling sound and tripping the RMS protection on the amp. I've disconnected the motor and the table moves freely. No binding or lack of lube.
I swapped the X and Y amps and the problem stays with the motor.
Running the motor disconnected from the lead screw, it vibrates badly and acts like the PID loop is horribly tuned. Without the power on, the motor turns smoothly by hand.
Using the linuxcnc halmeter and watching the encoder output while I turn it by hand I see normal encoder output (as far as I can tell).
I pulled the brushes and they seem to have life in them but I honestly don't know what they should look like.
I'm running out of ideas. Anyone point me in a direction?